1. Field of the Invention
The present invention relates to a magnetic disk drive apparatus. More specifically, the present invention relates to magnetic disk drive apparatus which provides an improved reliability in reading out data from magnetic disks.
2. Prior Art
In the past, magnetic disk drive apparatus have incorporated gate circuitry in order to eliminate data errors caused by electrical interference and the like. With such devices, the gate circuitry sets threshold values. Error bits having an amplitude lower than the preset threshold value are then eliminated.
There is inevitably a variation in the recording characteristics of the magnetic heads or media. The variation may result in a variation in the amplitude or other qualities of the read back data and makes it difficult to set appropriate threshold values. For example, if the threshold values are optimized for an area of the magnetic media where the read back signals are of a relatively low amplitude, then in regions where the read back signals are of a relatively high amplitude, error bits are likely to occur. Conversely, if the threshold values are optimized for an area of the magnetic media where the read back signals are of a relatively high amplitude, in regions where the read back signals are of low amplitude, loss of data is likely to occur. If an intermediate value is chosen, then both problems may occur.